The present invention relates to methods of connecting suspension assembly members together on a crane, such as mobile lift crane, and a frame mounted assembly used in such methods. Particularly the present invention relates to methods of moving connectors used to connect suspension straps between a stowed position and an operational position.
Lift cranes typically include a carbody; ground engaging members elevating the carbody off the ground; a rotating bed rotatably connected to the carbody such that the rotating bed can swing with respect to the ground engaging members; and a boom pivotally mounted on the rotating bed, with a load hoist line extending there from. For mobile lift cranes, there are different types of moveable ground engaging members, most notably tires for truck mounted cranes, and crawlers. Typically mobile lift cranes include a counterweight to help balance the crane when the crane lifts a load. Typical cranes include a boom suspension that is used to change the angle of the boom and provide tension forces to offset the forces applied to the boom by the load on the load hoist line so that the boom can behave as a column member with only compressive forces acting through the length of the boom. Typical cranes are designed to be set up with different boom length configurations to optimize the capacity that the crane can handle, only using as long of a boom as is necessary for a particular lift operation that the crane is being set up for. Since the boom length will vary between different configurations, the boom suspension also has to be designed to accommodate different boom lengths. Typically the boom suspension includes multiple sections of suspension members that are connected together, sometimes referred to as boom backstay straps, which connect between the top of the boom and either an equalizer suspended between the boom and a fixed mast, or between the boom and the top of a live mast. On a typical crane with a fixed mast, the boom hoist rigging comprises multiple parts of line that run between the equalizer and the top of the mast, and is used to control the angle of the boom.
When the crane needs to work on particularly high buildings or structures, or in restricted spaces, a jib may be mourned at the top of the boom to provide required reach. This could be a fixed jib or a luffing jib. When a jib is employed, one or more jib struts are connected to the top of the boom or bottom of the jib. These struts support the jib rigging and provide a moment arm about which force can be applied to support a load being lifted by the jib. When a luffing jib is used, frequently two struts will be used, and the angle between the struts will be controlled by jib hoist rigging. Changing the angle between the two struts will thus change the angle between the boom and the luffing jib.
When a jib is used on a crane, a jib suspension, typically in the form of backstay straps, is connected between the jib strut and the rotating bed, typically by being connected to the boom butt, which of course is pivotally connected to the rotating bed. These straps, like the straps in the typical boom suspension, are made of several separate sections.
Since the crane will be used in various locations, it needs to be designed so that it can be transported from one job site to the next. This usually requires that the crane be dismantled into components that are of a size and weight that they can be transported by truck within highway transportation limits. The ease with which the crane can be dismantled and set up has an impact on the total cost of using the crane. Thus, to the extent that fewer man-hours are needed to set up the crane, there is a direct advantage to the crane owner or renter.
It is convenient to transport the sections of the boom straps and jib backstay straps with the sections of boom between one job site and the next. This is because, for the most part, the number of sections and the length of each section of the boom straps and the jib backstay straps that will be needed are dependent on the number and lengths of the boom sections that are used to construct the boom. For example, a 100 foot boom may be made from a 10 foot boom butt, a 10 foot boom top and four 20 foot boom inserts. However, if the boom is going to be 120 feet long, five 20 foot boom inserts will be used. If the boom is going to be 130 feet long, five 20 foot inserts and one 10 foot insert will be used. For each of these different boom configurations, different numbers and lengths of sections of the boom straps and jib backstay straps will be used. However, it is convenient if the straps are transported between job sites on the tops of the boom sections where they can be easily connected together to make up the boom straps and jib backstay straps when the sections of boom are put together.
Typically the sections of the boom straps and jib backstay straps are connected together at the job site with connectors. The connectors typically have two holes through them, and the sections of the boom straps and jib backstay straps have a hole on each end. The sections of the boom straps or jib backstay straps are connected to one another by placing a pin though one hole of a connector and the hole in the end of one strap, and another pin through the other hole of the connector and the hole in the end of another section.
It is convenient when disassembling a crane to leave the connectors attached to one of the strap sections, so that the connection between that connector and that strap section does not have to be remade when the crane is assembled again. It is also convenient, when transporting the sections of straps on top of the boom sections, to pivot the connectors 180° from their operational position so that the combined strap section and connector is shorter than if the connector stayed at its operational position. In this position the connector can easily be secured to the strap or the boom section to prevent it from rotating during transport.
When it is time to set up the boom, it is necessary to flip each of the connectors from its stowed position to its operational position. Since each boom section will typically use a suspension where the straps are located on both the left and right sides of the boom, this means that there are two connectors that have to be flipped for every boom section. If the crane will be set up with a jib, there are also two connectors on the jib backstay sections for every boom section. The crane may use other suspension assemblies, such as to support a mast, that will also include multiple sections of suspension assembly, each with a connector between them that needs to be flipped from a stored position to an operation position. Also, typically the connectors are made of multiple link plates so that there are two link plates sandwiching the end of each suspension section.
Thus the crane assembly and disassembly process typically involves, among other things, many repetitive motions of flipping the link plates of the connectors connecting the suspension assemblies on the crane. When the crane is a small size, and the individual connector link plates do not weigh very much, this has not presented much of a problem. However, in larger cranes, each section of the boom suspension may be made of two separate straps, connected together by a connector that has three link plates, and each of these link plates may weigh a hundred pounds or more. Trying to flip the many heavy link plates by hand is not only time consuming, but it may not be safe for an assembly worker to lift more than 50 pounds. Thus it has been typical when setting up or taking apart boom sections for large cranes to use an assist crane to provide the lifting force required to move the connectors between a stowed position and an operational position.
When an assist crane is used, the multiple link plates of each connector can be flipped together. However, the use of an assist crane adds to the expense of setting up and taking down the crane, both because of the rental time for the assist crane and for the salary of the additional assemble person needed to operate the assist crane. Therefore there would be a great benefit if a method were invented of flipping the connector link plates so that the multiple link plates of each connector could be safely flipped at the same time and there was no need for an assist crane and an extra assembly worker. Further, by shortening the amount of time it takes to make each connection between the sections of the crane suspension by even just minutes, the total time for assembling the boom can be shortened by hours, since multiple connections have to be made.